yasnippet global mode not active when visiting a markdown buffer

[Luca Ferrari]

Hi all,
in my configuration I've:

  (use-package markdown-mode
    :ensure t
    :init
    (setq markdown-command "multimarkdown"))

(use-package yasnippet
  :ensure t)

(add-hook 'prog-mode-hook #'yas-minor-mode)


(global-set-key (kbd "C-c s n") 'yas-new-snippet)
(global-set-key (kbd "C-c s i") 'yas-insert-snippet)
(global-set-key (kbd "C-c s v") 'yas-visit-snippet-file)

(use-package yasnippet-snippets :ensure t)
(yas-global-mode 1)

However, whenever I visit a markdown file the yas-globa-mode is always
toggled off, and I've to automatically enable it. Moreover, even after
enabling it, the keybindings are the default ones, not the global one
I've set up.
What am I missing here?

Thanks,
Luca